Filter for removing particles from a gas stream and method for the manufacture thereof

Abstract

A filter for removing particles from a gas stream, in particular soot particulate from an exhaust-gas stream of an internal combustion engine, including a filter body composed of a ceramic filter substrate, the filter substrate being coated with a porous protective layer of a coating material. The coating material contains an admixture of 1 to 20% by weight of at least one compound of an element of the second main group, which may be of an oxide of an element of the second main group, and cracks contained in the ceramic filter substrate are partially filled with the coating material. In addition, a method for manufacturing a filter, where the coating material for the porous protective layer is applied to the sintered, ceramic filter substrate, at least one compound of an element of the second main group is added, optionally other substances contained in the protective layer are added, and the porous protective layer is fixed.

1 - 16 . (canceled) 
     
     
         17 . A filter for removing particles from a gas stream, comprising:
 a ceramic filter substrate; and   a filter body having the ceramic filter substrate so as to provide a filter substrate, wherein the filter substrate is coated with a porous protective layer of a coating material, wherein the coating material contains an admixture of 1 to 20% by weight of at least one compound of an element of a second main group, and wherein cracks contained in the ceramic filter substrate are partially filled with the coating material.   
     
     
         18 . The filter of  claim 17 , wherein the coating material for the porous protective layer is selected from the group consisting of aluminum oxide, aluminum hydroxide, titanium dioxide, silicon dioxide, zirconium dioxide, cerium dioxide, aluminum silicates, magnesium aluminum silicates, cordierite, mullites, silicon carbide, aluminum titanate, zeolites, quartz, glass, and blends and mixed oxides thereof. 
     
     
         19 . The filter of  claim 18 , wherein the coating material for the porous protective layer also includes at least one of an alkali metal compound and an alkali metal oxide. 
     
     
         20 . The filter of  claim 17 , wherein the coating material for the porous protective layer also contains at least one compound of an element of the third to the fifth B group or of the lanthanoids, including the lanthanum. 
     
     
         21 . The filter of  claim 17 , wherein at least one further porous protective layer is deposited on the porous protective layer. 
     
     
         22 . The filter of  claim 21 , wherein the porous protective layers, which are deposited one over the other, fulfill different functions. 
     
     
         23 . The filter of  claim 17 , wherein at least one of the porous protective layers contains a catalytically active component, preferably a metal or a plurality of metals from the group of the platinum metals, preferably platinum and/or palladium. 
     
     
         24 . The filter of  claim 17 , wherein the at least one porous protective layer is deposited at least one of in an outflow side and in a center region of the filter. 
     
     
         25 . The filter of  claim 17 , wherein the at least one porous protective layer is deposited at least one of in an inflow side and in a radially outer region of the filter. 
     
     
         26 . The filter of  claim 17 , wherein individual regions of the filter substrate are coated with different layers, quantities or layer sequences. 
     
     
         27 . A method for manufacturing a filter for removing particles from a gas stream, the method comprising:
 (a) adding at least one compound of an element of the second main group in the form of at least one of a solid and one of a gel, a salt solution and a hydrosol;   (b) applying a coating material for a porous protective layer to a sintered, ceramic filter substrate;   (c) optionally adding other substances contained in the protective layer; and   (d) fixing the porous protective layer;   wherein the filter includes a filter body having the ceramic filter substrate so as to provide a filter substrate, wherein the filter substrate is coated with a porous protective layer of a coating material, wherein the coating material contains an admixture of 1 to 20% by weight of at least one compound of an element of the second main group, and wherein cracks contained in the ceramic filter substrate are partially filled with the coating material   
     
     
         28 . The method of  claim 27 , wherein, in the pulverulent form, the coating material has a BET surface of more than 10 m 2 /g and a pore volume in the range of 0.1 to 1.5 ml/g. 
     
     
         29 . The method of  claim 27 , wherein the coating material has a particle size within the range of 2 nm to 20 μm. 
     
     
         30 . The method of  claim 27 , wherein the porous protective layer is applied in a sol-gel process, as a preformed sol or gel, or as a suspension of solid particles. 
     
     
         31 . The method of  claim 27 , wherein the at least one compound of an element of the second main group, as well as the other substances optionally contained in the coating are added to the raw material of the coating material, the coating mass or the finished coating. 
     
     
         32 . The method of  claim 27 , wherein at least one further porous protective layer is deposited onto the first porous protective layer, either each porous protective layer being initially fixed before the coating material of the subsequent layer is deposited, or the coating material for at least two layers being first deposited and subsequently jointly fixed. 
     
     
         33 . The method of  claim 27 , wherein the coating material has a particle size greater than 1 μm. 
     
     
         34 . The filter of  claim 17 , wherein the particles are soot particulate from an exhaust-gas stream of an internal combustion engine. 
     
     
         35 . The filter of  claim 17 , wherein the at least one compound includes an oxide of the element. 
     
     
         36 . The filter of  claim 20 , wherein the coating material for the porous protective layer also contains at least one compound of an oxide of the third to the fifth B group or of the lanthanoids, including the lanthanum. 
     
     
         37 . The filter of  claim 23 , wherein the catalytically active component includes a metal or a plurality of metals from the group of the platinum metals. 
     
     
         38 . The filter of  claim 23 , wherein the catalytically active component includes a metal or a plurality of metals from at least one of platinum and palladium.